xref: /device/generic/vulkan-cereal/protocols/vulkan/chapters/vertexpostproc.txt

// Copyright 2015-2021 The Khronos Group, Inc.
//
// SPDX-License-Identifier: CC-BY-4.0

[[vertexpostproc]]
= Fixed-Function Vertex Post-Processing

After <<pipeline-graphics-subsets-pre-rasterization,pre-rasterization shader
stages>>, the following fixed-function operations are applied to vertices of
the resulting primitives:

ifdef::VK_EXT_transform_feedback[]
  * Transform feedback (see <<vertexpostproc-transform-feedback,Transform
    Feedback>>)
endif::VK_EXT_transform_feedback[]
ifdef::VK_NV_viewport_swizzle[]
  * Viewport swizzle (see <<vertexpostproc-viewport-swizzle,Viewport
    Swizzle>>)
endif::VK_NV_viewport_swizzle[]
  * Flat shading (see <<vertexpostproc-flatshading>>).
  * Primitive clipping, including client-defined half-spaces (see
    <<vertexpostproc-clipping,Primitive Clipping>>).
  * Shader output attribute clipping (see
    <<vertexpostproc-clipping-shader-outputs,Clipping Shader Outputs>>).
ifdef::VK_NV_clip_space_w_scaling[]
  * Clip space W scaling (see <<vertexpostproc-viewportwscaling,Controlling
    Viewport W Scaling>>).
endif::VK_NV_clip_space_w_scaling[]
  * Perspective division on clip coordinates (see
    <<vertexpostproc-coord-transform,Coordinate Transformations>>).
  * Viewport mapping, including depth range scaling (see
    <<vertexpostproc-viewport,Controlling the Viewport>>).
  * Front face determination for polygon primitives (see
    <<primsrast-polygons-basic,Basic Polygon Rasterization>>).

ifdef::editing-notes[]
[NOTE]
.editing-note
====
TODO:Odd that this one link to a different chapter is in this list.
====
endif::editing-notes[]

Next, rasterization is performed on primitives as described in chapter
<<primsrast,Rasterization>>.


ifdef::VK_EXT_transform_feedback[]
[[vertexpostproc-transform-feedback]]
== Transform Feedback

Before any other fixed-function vertex post-processing, vertex outputs from
the last shader in the
<<pipeline-graphics-subsets-pre-rasterization,pre-rasterization shader
stage>> can: be written out to one or more transform feedback buffers bound
to the command buffer.
To capture vertex outputs the last
<<pipeline-graphics-subsets-pre-rasterization,pre-rasterization shader
stage>> shader must: be declared with the code:Xfb execution mode.
Outputs decorated with code:XfbBuffer will be written out to the
corresponding transform feedback buffers bound to the command buffer when
transform feedback is active.
Transform feedback buffers are bound to the command buffer by using
flink:vkCmdBindTransformFeedbackBuffersEXT.
Transform feedback is made active by calling
flink:vkCmdBeginTransformFeedbackEXT and made inactive by calling
flink:vkCmdEndTransformFeedbackEXT.
After vertex data is written it is possible to use
flink:vkCmdDrawIndirectByteCountEXT to start a new draw where the
pname:vertexCount is derived from the number of bytes written by a previous
transform feedback.

When an individual point, line, or triangle primitive reaches the transform
feedback stage while transform feedback is active, the values of the
specified output variables are assembled into primitives and appended to the
bound transform feedback buffers.
After activating transform feedback, the values of the first assembled
primitive are written at the starting offsets of the bound transform
feedback buffers, and subsequent primitives are appended to the buffer.
If the optional pname:pCounterBuffers and pname:pCounterBufferOffsets
parameters are specified, the starting points within the transform feedback
buffers are adjusted so data is appended to the previously written values
indicated by the value stored by the implementation in the counter buffer.

For multi-vertex primitives, all values for a given vertex are written
before writing values for any other vertex.
ifdef::VK_EXT_provoking_vertex[]
When
<<features-transformFeedbackPreservesProvokingVertex,transformFeedbackPreservesProvokingVertex>>
is not enabled, implementations
endif::VK_EXT_provoking_vertex[]
ifndef::VK_EXT_provoking_vertex[]
Implementations
endif::VK_EXT_provoking_vertex[]
may: write out any vertex within the primitive first, but all subsequent
vertices for that primitive must: be written out in a consistent winding
order defined as follows:

  * If neither <<geometry,geometry>> or <<tessellation,tessellation
    shading>> is active, vertices within a primitive are appended according
    to the winding order described by the <<drawing-primitive-topologies,
    primitive topology>> defined by the
    slink:VkPipelineInputAssemblyStateCreateInfo:pname:topology used to
    execute the <<drawing,drawing command>>.
  * If <<geometry,geometry shading>> is active, vertices within a primitive
    are appended according to the winding order described by the
    <<drawing-primitive-topologies, primitive topology>> defined by the
    <<drawing-point-lists, code:OutputPoints>>, <<drawing-line-strips,
    code:OutputLineStrips>>, or <<drawing-triangle-strips,
    code:OutputTriangleStrips>> execution mode.
  * If <<tessellation,tessellation shading>> is active but
    <<geometry,geometry shading>> is not, vertices within a primitive are
    appended according to the winding order defined by
    <<tessellation-triangle-tessellation, triangle tessellation>>,
    <<tessellation-quad-tessellation, quad tessellation>>, and
    <<tessellation-isoline-tessellation, isoline tessellation>>.

ifdef::VK_EXT_provoking_vertex[]
When
<<features-transformFeedbackPreservesProvokingVertex,transformFeedbackPreservesProvokingVertex>>
is enabled, then in addition to writing vertices with a consistent winding
order, the vertex order must: preserve the <<vertexpostproc-flatshading,
provoking vertex>> of each primitive:

  * When the
    <<VkPipelineRasterizationProvokingVertexStateCreateInfoEXT,pipeline's
    provoking vertex mode>> is
    ename:VK_PROVOKING_VERTEX_MODE_FIRST_VERTEX_EXT, the primitive's
    provoking vertex must be the first vertex written.
  * When the
    <<VkPipelineRasterizationProvokingVertexStateCreateInfoEXT,pipeline's
    provoking vertex mode>> is
    ename:VK_PROVOKING_VERTEX_MODE_LAST_VERTEX_EXT, the primitive's
    provoking vertex must be the last vertex written.

If
<<limits-transformFeedbackPreservesTriangleFanProvokingVertex,pname:transformFeedbackPreservesTriangleFanProvokingVertex>>
is ename:VK_FALSE, neither <<geometry,geometry>> nor
<<tessellation,tessellation>> shading is active, and the
<<drawing-primitive-topologies,primitive topology>> is
ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_FAN, then the first vertex written from
each primitive is implementation-defined even when
<<features-transformFeedbackPreservesProvokingVertex,transformFeedbackPreservesProvokingVertex>>
is enabled.

endif::VK_EXT_provoking_vertex[]

When capturing vertices, the stride associated with each transform feedback
buffer, as indicated by the code:XfbStride decoration, indicates the number
of bytes of storage reserved for each vertex in the transform feedback
buffer.
For every vertex captured, each output attribute with a code:Offset
decoration will be written to the storage reserved for the vertex at the
associated transform feedback buffer.
When writing output variables that are arrays or structures, individual
array elements or structure members are written tightly packed in order.
For vector types, individual components are written in order.
For matrix types, outputs are written as an array of column vectors.

If any component of an output with an assigned transform feedback offset was
not written to by its shader, the value recorded for that component is
undefined:.
All components of an output variable must: be written at an offset aligned
to the size of the component.
The size of each component of an output variable must: be at least 32-bits.
When capturing a vertex, any portion of the reserved storage not associated
with an output variable with an assigned transform feedback offset will be
unmodified.

When transform feedback is inactive, no vertices are recorded.
If there is a valid counter buffer handle and counter buffer offset in the
pname:pCounterBuffers and pname:pCounterBufferOffsets arrays, writes to the
corresponding transform feedback buffer will start at the byte offset
represented by the value stored in the counter buffer location.

Individual lines or triangles of a strip or fan primitive will be extracted
and recorded separately.
Incomplete primitives are not recorded.

When using a geometry shader that emits vertices to multiple vertex streams,
a primitive will be assembled and output for each stream when there are
enough vertices emitted for the output primitive type.
All outputs assigned to a given transform feedback buffer are required to
come from a single vertex stream.

The sizes of the transform feedback buffers are defined by the
flink:vkCmdBindTransformFeedbackBuffersEXT pname:pSizes parameter for each
of the bound buffers, or the size of the bound buffer, whichever is the
lesser.
If there is less space remaining in any of the transform feedback buffers
than the size of all of the vertex data for that primitive based on the
code:XfbStride for that code:XfbBuffer then no vertex data of that primitive
is recorded in any transform feedback buffer, and the value for the number
of primitives written in the corresponding
ename:VK_QUERY_TYPE_TRANSFORM_FEEDBACK_STREAM_EXT query for all transform
feedback buffers is no longer incremented.

Any outputs made to a code:XfbBuffer that is not bound to a transform
feedback buffer is ignored.

[open,refpage='vkCmdBindTransformFeedbackBuffersEXT',desc='Bind transform feedback buffers to a command buffer',type='protos']
--
To bind transform feedback buffers to a command buffer for use in subsequent
drawing commands, call:

include::{generated}/api/protos/vkCmdBindTransformFeedbackBuffersEXT.txt[]

  * pname:commandBuffer is the command buffer into which the command is
    recorded.
  * pname:firstBinding is the index of the first transform feedback binding
    whose state is updated by the command.
  * pname:bindingCount is the number of transform feedback bindings whose
    state is updated by the command.
  * pname:pBuffers is a pointer to an array of buffer handles.
  * pname:pOffsets is a pointer to an array of buffer offsets.
  * pname:pSizes is `NULL` or a pointer to an array of basetype:VkDeviceSize
    buffer sizes, specifying the maximum number of bytes to capture to the
    corresponding transform feedback buffer.
    If pname:pSizes is `NULL`, or the value of the pname:pSizes array
    element is ename:VK_WHOLE_SIZE, then the maximum number of bytes
    captured will be the size of the corresponding buffer minus the buffer
    offset.

The values taken from elements [eq]#i# of pname:pBuffers, pname:pOffsets and
pname:pSizes replace the current state for the transform feedback binding
[eq]#pname:firstBinding {plus} i#, for [eq]#i# in [eq]#[0,
pname:bindingCount)#.
The transform feedback binding is updated to start at the offset indicated
by pname:pOffsets[i] from the start of the buffer pname:pBuffers[i].

.Valid Usage
****
  * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-transformFeedback-02355]]
    sname:VkPhysicalDeviceTransformFeedbackFeaturesEXT::pname:transformFeedback
    must: be enabled
  * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-firstBinding-02356]]
    pname:firstBinding must: be less than
    sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBuffers
  * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-firstBinding-02357]]
    The sum of pname:firstBinding and pname:bindingCount must: be less than
    or equal to
    sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBuffers
  * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pOffsets-02358]]
    All elements of pname:pOffsets must: be less than the size of the
    corresponding element in pname:pBuffers
  * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pOffsets-02359]]
    All elements of pname:pOffsets must: be a multiple of 4
  * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pBuffers-02360]]
    All elements of pname:pBuffers must: have been created with the
    ename:VK_BUFFER_USAGE_TRANSFORM_FEEDBACK_BUFFER_BIT_EXT flag
  * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pSize-02361]]
    If the optional pname:pSize array is specified, each element of
    pname:pSizes must: either be ename:VK_WHOLE_SIZE, or be less than or
    equal to
    sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBufferSize
  * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pSizes-02362]]
    All elements of pname:pSizes must: be either ename:VK_WHOLE_SIZE, or
    less than or equal to the size of the corresponding buffer in
    pname:pBuffers
  * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pOffsets-02363]]
    All elements of pname:pOffsets plus pname:pSizes, where the
    pname:pSizes, element is not ename:VK_WHOLE_SIZE, must: be less than or
    equal to the size of the corresponding buffer in pname:pBuffers
  * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-pBuffers-02364]]
    Each element of pname:pBuffers that is non-sparse must: be bound
    completely and contiguously to a single sname:VkDeviceMemory object
  * [[VUID-vkCmdBindTransformFeedbackBuffersEXT-None-02365]]
    Transform feedback must: not be active when the
    fname:vkCmdBindTransformFeedbackBuffersEXT command is recorded
****

include::{generated}/validity/protos/vkCmdBindTransformFeedbackBuffersEXT.txt[]
--

[open,refpage='vkCmdBeginTransformFeedbackEXT',desc='Make transform feedback active in the command buffer',type='protos']
--
Transform feedback for specific transform feedback buffers is made active by
calling:

include::{generated}/api/protos/vkCmdBeginTransformFeedbackEXT.txt[]

  * pname:commandBuffer is the command buffer into which the command is
    recorded.
  * pname:firstCounterBuffer is the index of the first transform feedback
    buffer corresponding to pname:pCounterBuffers[0] and
    pname:pCounterBufferOffsets[0].
  * pname:counterBufferCount is the size of the pname:pCounterBuffers and
    pname:pCounterBufferOffsets arrays.
  * pname:pCounterBuffers is `NULL` or a pointer to an array of
    slink:VkBuffer handles to counter buffers.
    Each buffer contains a 4 byte integer value representing the byte offset
    from the start of the corresponding transform feedback buffer from where
    to start capturing vertex data.
    If the byte offset stored to the counter buffer location was done using
    flink:vkCmdEndTransformFeedbackEXT it can be used to resume transform
    feedback from the previous location.
    If pname:pCounterBuffers is `NULL`, then transform feedback will start
    capturing vertex data to byte offset zero in all bound transform
    feedback buffers.
    For each element of pname:pCounterBuffers that is dlink:VK_NULL_HANDLE,
    transform feedback will start capturing vertex data to byte zero in the
    corresponding bound transform feedback buffer.
  * pname:pCounterBufferOffsets is `NULL` or a pointer to an array of
    basetype:VkDeviceSize values specifying offsets within each of the
    pname:pCounterBuffers where the counter values were previously written.
    The location in each counter buffer at these offsets must: be large
    enough to contain 4 bytes of data.
    This data is the number of bytes captured by the previous transform
    feedback to this buffer.
    If pname:pCounterBufferOffsets is `NULL`, then it is assumed the offsets
    are zero.

The active transform feedback buffers will capture primitives emitted from
the corresponding code:XfbBuffer in the bound graphics pipeline.
Any code:XfbBuffer emitted that does not output to an active transform
feedback buffer will not be captured.

.Valid Usage
****
  * [[VUID-vkCmdBeginTransformFeedbackEXT-transformFeedback-02366]]
    sname:VkPhysicalDeviceTransformFeedbackFeaturesEXT::pname:transformFeedback
    must: be enabled
  * [[VUID-vkCmdBeginTransformFeedbackEXT-None-02367]]
    Transform feedback must: not be active
  * [[VUID-vkCmdBeginTransformFeedbackEXT-firstCounterBuffer-02368]]
    pname:firstCounterBuffer must: be less than
    sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBuffers
  * [[VUID-vkCmdBeginTransformFeedbackEXT-firstCounterBuffer-02369]]
    The sum of pname:firstCounterBuffer and pname:counterBufferCount must:
    be less than or equal to
    sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBuffers
  * [[VUID-vkCmdBeginTransformFeedbackEXT-counterBufferCount-02607]]
    If pname:counterBufferCount is not `0`, and pname:pCounterBuffers is not
    `NULL`, pname:pCounterBuffers must: be a valid pointer to an array of
    pname:counterBufferCount sname:VkBuffer handles that are either valid or
    dlink:VK_NULL_HANDLE
  * [[VUID-vkCmdBeginTransformFeedbackEXT-pCounterBufferOffsets-02370]]
    For each buffer handle in the array, if it is not dlink:VK_NULL_HANDLE
    it must: reference a buffer large enough to hold 4 bytes at the
    corresponding offset from the pname:pCounterBufferOffsets array
  * [[VUID-vkCmdBeginTransformFeedbackEXT-pCounterBuffer-02371]]
    If pname:pCounterBuffer is `NULL`, then pname:pCounterBufferOffsets
    must: also be `NULL`
  * [[VUID-vkCmdBeginTransformFeedbackEXT-pCounterBuffers-02372]]
    For each buffer handle in the pname:pCounterBuffers array that is not
    dlink:VK_NULL_HANDLE it must: have been created with a pname:usage value
    containing
    ename:VK_BUFFER_USAGE_TRANSFORM_FEEDBACK_COUNTER_BUFFER_BIT_EXT
  * [[VUID-vkCmdBeginTransformFeedbackEXT-None-06233]]
    A valid graphics pipeline must: be bound to
    ename:VK_PIPELINE_BIND_POINT_GRAPHICS
  * [[VUID-vkCmdBeginTransformFeedbackEXT-None-04128]]
    The last <<pipeline-graphics-subsets-pre-rasterization,pre-rasterization
    shader stage>> of the bound graphics pipeline must: have been declared
    with the code:Xfb execution mode
ifdef::VK_VERSION_1_1,VK_KHR_multiview[]
  * [[VUID-vkCmdBeginTransformFeedbackEXT-None-02373]]
    Transform feedback must: not be made active in a render pass instance
    with multiview enabled
endif::VK_VERSION_1_1,VK_KHR_multiview[]
****

include::{generated}/validity/protos/vkCmdBeginTransformFeedbackEXT.txt[]
--

[open,refpage='vkCmdEndTransformFeedbackEXT',desc='Make transform feedback inactive in the command buffer',type='protos']
--
Transform feedback for specific transform feedback buffers is made inactive
by calling:

include::{generated}/api/protos/vkCmdEndTransformFeedbackEXT.txt[]

  * pname:commandBuffer is the command buffer into which the command is
    recorded.
  * pname:firstCounterBuffer is the index of the first transform feedback
    buffer corresponding to pname:pCounterBuffers[0] and
    pname:pCounterBufferOffsets[0].
  * pname:counterBufferCount is the size of the pname:pCounterBuffers and
    pname:pCounterBufferOffsets arrays.
  * pname:pCounterBuffers is `NULL` or a pointer to an array of
    slink:VkBuffer handles to counter buffers.
    The counter buffers are used to record the current byte positions of
    each transform feedback buffer where the next vertex output data would
    be captured.
    This can: be used by a subsequent flink:vkCmdBeginTransformFeedbackEXT
    call to resume transform feedback capture from this position.
    It can also be used by flink:vkCmdDrawIndirectByteCountEXT to determine
    the vertex count of the draw call.
  * pname:pCounterBufferOffsets is `NULL` or a pointer to an array of
    basetype:VkDeviceSize values specifying offsets within each of the
    pname:pCounterBuffers where the counter values can be written.
    The location in each counter buffer at these offsets must: be large
    enough to contain 4 bytes of data.
    The data stored at this location is the byte offset from the start of
    the transform feedback buffer binding where the next vertex data would
    be written.
    If pname:pCounterBufferOffsets is `NULL`, then it is assumed the offsets
    are zero.

.Valid Usage
****
  * [[VUID-vkCmdEndTransformFeedbackEXT-transformFeedback-02374]]
    sname:VkPhysicalDeviceTransformFeedbackFeaturesEXT::pname:transformFeedback
    must: be enabled
  * [[VUID-vkCmdEndTransformFeedbackEXT-None-02375]]
    Transform feedback must: be active
  * [[VUID-vkCmdEndTransformFeedbackEXT-firstCounterBuffer-02376]]
    pname:firstCounterBuffer must: be less than
    sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBuffers
  * [[VUID-vkCmdEndTransformFeedbackEXT-firstCounterBuffer-02377]]
    The sum of pname:firstCounterBuffer and pname:counterBufferCount must:
    be less than or equal to
    sname:VkPhysicalDeviceTransformFeedbackPropertiesEXT::pname:maxTransformFeedbackBuffers
  * [[VUID-vkCmdEndTransformFeedbackEXT-counterBufferCount-02608]]
    If pname:counterBufferCount is not `0`, and pname:pCounterBuffers is not
    `NULL`, pname:pCounterBuffers must: be a valid pointer to an array of
    pname:counterBufferCount sname:VkBuffer handles that are either valid or
    dlink:VK_NULL_HANDLE
  * [[VUID-vkCmdEndTransformFeedbackEXT-pCounterBufferOffsets-02378]]
    For each buffer handle in the array, if it is not dlink:VK_NULL_HANDLE
    it must: reference a buffer large enough to hold 4 bytes at the
    corresponding offset from the pname:pCounterBufferOffsets array
  * [[VUID-vkCmdEndTransformFeedbackEXT-pCounterBuffer-02379]]
    If pname:pCounterBuffer is `NULL`, then pname:pCounterBufferOffsets
    must: also be `NULL`
  * [[VUID-vkCmdEndTransformFeedbackEXT-pCounterBuffers-02380]]
    For each buffer handle in the pname:pCounterBuffers array that is not
    dlink:VK_NULL_HANDLE it must: have been created with a pname:usage value
    containing
    ename:VK_BUFFER_USAGE_TRANSFORM_FEEDBACK_COUNTER_BUFFER_BIT_EXT
****

include::{generated}/validity/protos/vkCmdEndTransformFeedbackEXT.txt[]
--
endif::VK_EXT_transform_feedback[]


ifdef::VK_NV_viewport_swizzle[]
[[vertexpostproc-viewport-swizzle]]
== Viewport Swizzle

[open,refpage='VkPipelineViewportSwizzleStateCreateInfoNV',desc='Structure specifying swizzle applied to primitive clip coordinates',type='structs']
--
Each primitive sent to a given viewport has a swizzle and optional: negation
applied to its clip coordinates.
The swizzle that is applied depends on the viewport index, and is controlled
by the sname:VkPipelineViewportSwizzleStateCreateInfoNV pipeline state:

include::{generated}/api/structs/VkPipelineViewportSwizzleStateCreateInfoNV.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:flags is reserved for future use.
  * pname:viewportCount is the number of viewport swizzles used by the
    pipeline.
  * pname:pViewportSwizzles is a pointer to an array of
    slink:VkViewportSwizzleNV structures, defining the viewport swizzles.

.Valid Usage
****
  * [[VUID-VkPipelineViewportSwizzleStateCreateInfoNV-viewportCount-01215]]
    pname:viewportCount must: be greater than or equal to the
    pname:viewportCount set in sname:VkPipelineViewportStateCreateInfo
****

include::{generated}/validity/structs/VkPipelineViewportSwizzleStateCreateInfoNV.txt[]
--

[open,refpage='VkPipelineViewportSwizzleStateCreateFlagsNV',desc='Reserved for future use',type='flags']
--
include::{generated}/api/flags/VkPipelineViewportSwizzleStateCreateFlagsNV.txt[]

tname:VkPipelineViewportSwizzleStateCreateFlagsNV is a bitmask type for
setting a mask, but is currently reserved for future use.
--

The sname:VkPipelineViewportSwizzleStateCreateInfoNV state is set by adding
this structure to the pname:pNext chain of a
sname:VkPipelineViewportStateCreateInfo structure and setting the graphics
pipeline state with flink:vkCreateGraphicsPipelines.

Each viewport specified from 0 to pname:viewportCount - 1 has its x,y,z,w
swizzle state set to the corresponding pname:x, pname:y, pname:z and pname:w
in the slink:VkViewportSwizzleNV structure.
Each component is of type elink:VkViewportCoordinateSwizzleNV, which
determines the type of swizzle for that component.
The value of pname:x computes the new x component of the position as:

[source,c]
---------------------------------------------------
if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_X_NV) x' = x;
if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_NEGATIVE_X_NV) x' = -x;
if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_Y_NV) x' = y;
if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_NEGATIVE_Y_NV) x' = -y;
if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_Z_NV) x' = z;
if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_NEGATIVE_Z_NV) x' = -z;
if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_W_NV) x' = w;
if (x == VK_VIEWPORT_COORDINATE_SWIZZLE_NEGATIVE_W_NV) x' = -w;
---------------------------------------------------

Similar selections are performed for the pname:y, pname:z, and pname:w
coordinates.
This swizzling is applied before clipping and perspective divide.
If the swizzle for an active viewport index is not specified, the swizzle
for pname:x is ename:VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_X_NV, pname:y
is ename:VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_Y_NV, pname:z is
ename:VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_Z_NV and pname:w is
ename:VK_VIEWPORT_COORDINATE_SWIZZLE_POSITIVE_W_NV.

Viewport swizzle parameters are specified by setting the pname:pNext pointer
of sname:VkGraphicsPipelineCreateInfo to point to a
sname:VkPipelineViewportSwizzleStateCreateInfoNV structure.
slink:VkPipelineViewportSwizzleStateCreateInfoNV uses
sname:VkViewportSwizzleNV to set the viewport swizzle parameters.

[open,refpage='VkViewportSwizzleNV',desc='Structure specifying a viewport swizzle',type='structs']
--
The sname:VkViewportSwizzleNV structure is defined as:

include::{generated}/api/structs/VkViewportSwizzleNV.txt[]

  * pname:x is a elink:VkViewportCoordinateSwizzleNV value specifying the
    swizzle operation to apply to the x component of the primitive
  * pname:y is a elink:VkViewportCoordinateSwizzleNV value specifying the
    swizzle operation to apply to the y component of the primitive
  * pname:z is a elink:VkViewportCoordinateSwizzleNV value specifying the
    swizzle operation to apply to the z component of the primitive
  * pname:w is a elink:VkViewportCoordinateSwizzleNV value specifying the
    swizzle operation to apply to the w component of the primitive

include::{generated}/validity/structs/VkViewportSwizzleNV.txt[]
--

[open,refpage='VkViewportCoordinateSwizzleNV',desc='Specify how a viewport coordinate is swizzled',type='enums']
--
Possible values of the slink:VkViewportSwizzleNV::pname:x, pname:y, pname:z,
and pname:w members, specifying swizzling of the corresponding components of
primitives, are:

include::{generated}/api/enums/VkViewportCoordinateSwizzleNV.txt[]

These values are described in detail in <<vertexpostproc-viewport-swizzle,
Viewport Swizzle>>.
--
endif::VK_NV_viewport_swizzle[]


[[vertexpostproc-flatshading]]
== Flat Shading

_Flat shading_ a vertex output attribute means to assign all vertices of the
primitive the same value for that output.
The output values assigned are those of the _provoking vertex_ of the
primitive.
Flat shading is applied to those vertex attributes that
<<interfaces-iointerfaces-matching,match>> fragment input attributes which
are decorated as code:Flat.

If neither <<geometry,geometry>> nor <<tessellation,tessellation shading>>
is active, the provoking vertex is determined by the
<<drawing-primitive-topologies, primitive topology>> defined by
slink:VkPipelineInputAssemblyStateCreateInfo:pname:topology used to execute
the <<drawing,drawing command>>.

If <<geometry,geometry shading>> is active, the provoking vertex is
determined by the <<drawing-primitive-topologies, primitive topology>>
defined by the <<drawing-point-lists, code:OutputPoints>>,
<<drawing-line-strips, code:OutputLineStrips>>, or
<<drawing-triangle-strips, code:OutputTriangleStrips>> execution mode.

If <<tessellation,tessellation shading>> is active but <<geometry,geometry
shading>> is not, the provoking vertex may: be any of the vertices in each
primitive.

ifdef::VK_EXT_provoking_vertex[]
[open,refpage='VkPipelineRasterizationProvokingVertexStateCreateInfoEXT',desc='Structure specifying provoking vertex mode used by a graphics pipeline',type='structs']
--
For a given primitive topology, the pipeline's provoking vertex mode
determines which vertex is the provoking vertex.
To specify the provoking vertex mode, include a
sname:VkPipelineRasterizationProvokingVertexStateCreateInfoEXT structure in
the slink:VkPipelineRasterizationStateCreateInfo::pname:pNext chain when
creating the pipeline.

The sname:VkPipelineRasterizationProvokingVertexStateCreateInfoEXT structure
is defined as:

include::{generated}/api/structs/VkPipelineRasterizationProvokingVertexStateCreateInfoEXT.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:provokingVertexMode is a elink:VkProvokingVertexModeEXT value
    selecting the provoking vertex mode.

If this struct is not provided when creating the pipeline, the pipeline will
use the ename:VK_PROVOKING_VERTEX_MODE_FIRST_VERTEX_EXT mode.

If the
<<limits-provokingVertexModePerPipeline,provokingVertexModePerPipeline>>
limit is ename:VK_FALSE, then all pipelines bound within a render pass
instance must: have the same pname:provokingVertexMode.

.Valid Usage
****
  * [[VUID-VkPipelineRasterizationProvokingVertexStateCreateInfoEXT-provokingVertexMode-04883]]
    If pname:provokingVertexMode is
    ename:VK_PROVOKING_VERTEX_MODE_LAST_VERTEX_EXT, then the
    <<features-provokingVertexLast,provokingVertexLast>> feature must: be
    enabled
****

include::{generated}/validity/structs/VkPipelineRasterizationProvokingVertexStateCreateInfoEXT.txt[]
--

[open,refpage='VkProvokingVertexModeEXT',desc='Specify which vertex in a primitive is the provoking vertex',type='enums']
--
Possible values of
slink:VkPipelineRasterizationProvokingVertexStateCreateInfoEXT::pname:provokingVertexMode
are:

include::{generated}/api/enums/VkProvokingVertexModeEXT.txt[]

  * ename:VK_PROVOKING_VERTEX_MODE_FIRST_VERTEX_EXT specifies that the
    provoking vertex is the first non-adjacency vertex in the list of
    vertices used by a primitive.
  * ename:VK_PROVOKING_VERTEX_MODE_LAST_VERTEX_EXT specifies that the
    provoking vertex is the last non-adjacency vertex in the list of
    vertices used by a primitive.

These modes are described more precisely in
<<drawing-primitive-topologies,Primitive Topologies>>.
--
endif::VK_EXT_provoking_vertex[]


[[vertexpostproc-clipping]]
== Primitive Clipping

Primitives are culled against the _cull volume_ and then clipped to the
_clip volume_.
In clip coordinates, the _view volume_ is defined by:

[latexmath]
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
\begin{array}{c}
-w_c \leq x_c \leq w_c \\
-w_c \leq y_c \leq w_c \\
0 \leq z_c \leq w_c
\end{array}
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

This view volume can: be further restricted by as many as
sname:VkPhysicalDeviceLimits::pname:maxClipDistances client-defined
half-spaces.

The cull volume is the intersection of up to
sname:VkPhysicalDeviceLimits::pname:maxCullDistances client-defined
half-spaces (if no client-defined cull half-spaces are enabled, culling
against the cull volume is skipped).

A shader must: write a single cull distance for each enabled cull half-space
to elements of the code:CullDistance array.
If the cull distance for any enabled cull half-space is negative for all of
the vertices of the primitive under consideration, the primitive is
discarded.
Otherwise the primitive is clipped against the clip volume as defined below.

The clip volume is the intersection of up to
sname:VkPhysicalDeviceLimits::pname:maxClipDistances client-defined
half-spaces with the view volume (if no client-defined clip half-spaces are
enabled, the clip volume is the view volume).

A shader must: write a single clip distance for each enabled clip half-space
to elements of the code:ClipDistance array.
Clip half-space [eq]#i# is then given by the set of points satisfying the
inequality

  {empty}:: [eq]#c~i~(**P**) {geq} 0#

where [eq]#c~i~(**P**)# is the clip distance [eq]#i# at point [eq]#**P**#.
For point primitives, [eq]#c~i~(**P**)# is simply the clip distance for the
vertex in question.
For line and triangle primitives, per-vertex clip distances are interpolated
using a weighted mean, with weights derived according to the algorithms
described in sections <<primsrast-lines-basic,Basic Line Segment
Rasterization>> and <<primsrast-polygons-basic,Basic Polygon
Rasterization>>, using the perspective interpolation equations.

The number of client-defined clip and cull half-spaces that are enabled is
determined by the explicit size of the built-in arrays code:ClipDistance and
code:CullDistance, respectively, declared as an output in the interface of
the entry point of the final shader stage before clipping.

ifdef::VK_EXT_depth_clip_enable[]
If slink:VkPipelineRasterizationDepthClipStateCreateInfoEXT is present in
the graphics pipeline state then depth clipping is disabled if
slink:VkPipelineRasterizationDepthClipStateCreateInfoEXT::pname:depthClipEnable
is ename:VK_FALSE.
Otherwise, if slink:VkPipelineRasterizationDepthClipStateCreateInfoEXT is
not present, depth clipping is disabled when
slink:VkPipelineRasterizationStateCreateInfo::pname:depthClampEnable is
ename:VK_TRUE.
endif::VK_EXT_depth_clip_enable[]
ifndef::VK_EXT_depth_clip_enable[]
Depth clamping is enabled or disabled via the pname:depthClampEnable enable
of the slink:VkPipelineRasterizationStateCreateInfo structure.
Depth clipping is disabled when pname:depthClampEnable is ename:VK_TRUE.
endif::VK_EXT_depth_clip_enable[]
When depth clipping is disabled, the plane equation

  {empty}:: [eq]#0 {leq} z~c~ {leq} w~c~#

(see the clip volume definition above) is ignored by view volume clipping
(effectively, there is no near or far plane clipping).

If the primitive under consideration is a point or line segment, then
clipping passes it unchanged if its vertices lie entirely within the clip
volume.

ifndef::VK_VERSION_1_1,VK_KHR_maintenance2[]
If a point's vertex lies outside of the clip volume, the entire primitive
may: be discarded.
endif::VK_VERSION_1_1,VK_KHR_maintenance2[]

ifdef::VK_VERSION_1_1,VK_KHR_maintenance2[]
[open,refpage='VkPointClippingBehavior',desc='Enum specifying the point clipping behavior',type='enums']
--
Possible values of
slink:VkPhysicalDevicePointClippingProperties::pname:pointClippingBehavior,
specifying clipping behavior of a point primitive whose vertex lies outside
the clip volume, are:

include::{generated}/api/enums/VkPointClippingBehavior.txt[]

ifdef::VK_KHR_maintenance2[]
or the equivalent

include::{generated}/api/enums/VkPointClippingBehaviorKHR.txt[]
endif::VK_KHR_maintenance2[]

  * ename:VK_POINT_CLIPPING_BEHAVIOR_ALL_CLIP_PLANES specifies that the
    primitive is discarded if the vertex lies outside any clip plane,
    including the planes bounding the view volume.
  * ename:VK_POINT_CLIPPING_BEHAVIOR_USER_CLIP_PLANES_ONLY specifies that
    the primitive is discarded only if the vertex lies outside any user clip
    plane.
--
endif::VK_VERSION_1_1,VK_KHR_maintenance2[]

If either of a line segment's vertices lie outside of the clip volume, the
line segment may: be clipped, with new vertex coordinates computed for each
vertex that lies outside the clip volume.
A clipped line segment endpoint lies on both the original line segment and
the boundary of the clip volume.

This clipping produces a value, [eq]#0 {leq} t {leq} 1#, for each clipped
vertex.
If the coordinates of a clipped vertex are [eq]#**P**# and the unclipped
line segment's vertex coordinates are [eq]#**P**~1~# and [eq]#**P**~2~#,
then [eq]#t# satisfies the following equation

  {empty}:: [eq]#**P** = t **P**~1~ {plus} (1-t) **P**~2~#.

[eq]#t# is used to clip vertex output attributes as described in
<<vertexpostproc-clipping-shader-outputs,Clipping Shader Outputs>>.

If the primitive is a polygon, it passes unchanged if every one of its edges
lies entirely inside the clip volume, and is either clipped or discarded
otherwise.
If the edges of the polygon intersect the boundary of the clip volume, the
intersecting edges are reconnected by new edges that lie along the boundary
of the clip volume - in some cases requiring the introduction of new
vertices into a polygon.

If a polygon intersects an edge of the clip volume's boundary, the clipped
polygon must: include a point on this boundary edge.

Primitives rendered with user-defined half-spaces must: satisfy a
complementarity criterion.
Suppose a series of primitives is drawn where each vertex [eq]#i# has a
single specified clip distance [eq]#d~i~# (or a number of similarly
specified clip distances, if multiple half-spaces are enabled).
Next, suppose that the same series of primitives are drawn again with each
such clip distance replaced by [eq]#-d~i~# (and the graphics pipeline is
otherwise the same).
In this case, primitives must: not be missing any pixels, and pixels must:
not be drawn twice in regions where those primitives are cut by the clip
planes.


[[vertexpostproc-clipping-shader-outputs]]
== Clipping Shader Outputs

Next, vertex output attributes are clipped.
The output values associated with a vertex that lies within the clip volume
are unaffected by clipping.
If a primitive is clipped, however, the output values assigned to vertices
produced by clipping are clipped.

Let the output values assigned to the two vertices [eq]#**P**~1~# and
[eq]#**P**~2~# of an unclipped edge be [eq]#**c**~1~# and [eq]#**c**~2~#.
The value of [eq]#t# (see <<vertexpostproc-clipping,Primitive Clipping>>)
for a clipped point [eq]#**P**# is used to obtain the output value
associated with [eq]#**P**# as

  {empty}:: [eq]#**c** = t **c**~1~ {plus} (1-t) **c**~2~#.

(Multiplying an output value by a scalar means multiplying each of _x_, _y_,
_z_, and _w_ by the scalar.)

Since this computation is performed in clip space before division by
[eq]#w~c~#, clipped output values are perspective-correct.

Polygon clipping creates a clipped vertex along an edge of the clip volume's
boundary.
This situation is handled by noting that polygon clipping proceeds by
clipping against one half-space at a time.
Output value clipping is done in the same way, so that clipped points always
occur at the intersection of polygon edges (possibly already clipped) with
the clip volume's boundary.

For vertex output attributes whose matching fragment input attributes are
decorated with code:NoPerspective, the value of [eq]#t# used to obtain the
output value associated with [eq]#**P**# will be adjusted to produce results
that vary linearly in framebuffer space.

Output attributes of integer or unsigned integer type must: always be flat
shaded.
Flat shaded attributes are constant over the primitive being rasterized (see
<<primsrast-lines-basic,Basic Line Segment Rasterization>> and
<<primsrast-polygons-basic,Basic Polygon Rasterization>>), and no
interpolation is performed.
The output value [eq]#**c**# is taken from either [eq]#**c**~1~# or
[eq]#**c**~2~#, since flat shading has already occurred and the two values
are identical.

ifdef::VK_NV_clip_space_w_scaling[]
include::VK_NV_clip_space_w_scaling/vertexpostproc.txt[]
endif::VK_NV_clip_space_w_scaling[]


[[vertexpostproc-coord-transform]]
== Coordinate Transformations

_Clip coordinates_ for a vertex result from shader execution, which yields a
vertex coordinate code:Position.

Perspective division on clip coordinates yields _normalized device
coordinates_, followed by a _viewport_ transformation (see
<<vertexpostproc-viewport,Controlling the Viewport>>) to convert these
coordinates into _framebuffer coordinates_.

If a vertex in clip coordinates has a position given by

[latexmath]
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
\left(\begin{array}{c}
x_c \\
y_c \\
z_c \\
w_c
\end{array}\right)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

then the vertex's normalized device coordinates are
[latexmath]
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
\left(
        \begin{array}{c}
                x_d \\
                y_d \\
                z_d
        \end{array}
\right) =
\left(
        \begin{array}{c}
                \frac{x_c}{w_c} \\
                \frac{y_c}{w_c} \\
                \frac{z_c}{w_c}
        \end{array}
\right)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


ifdef::VK_QCOM_render_pass_transform[]
[[vertexpostproc-renderpass-transform]]
== Render Pass Transform

A _render pass transform_ can: be enabled for render pass instances.
The clip coordinates [eq]#(x~c~, y~c~)# that result from vertex shader
execution are transformed by a rotation of 0, 90, 180, or 270 degrees in the
XY plane, centered at the origin.

When _Render pass transform_ is enabled, the transform applies to all
primitives for all subpasses of the render pass.
The transformed vertex in clip coordinates has a position given by

[latexmath]
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
\left(
        \begin{array}{c}
                x_{c_{trans}} \\
                y_{c_{trans}} \\
                z_{c_{trans}}
        \end{array}
\right) =
\left(
        \begin{array}{c}
                x_{c} \cos \theta - y_{c} \sin \theta \\
                x_{c} \sin \theta + y_{c} \cos \theta \\
                z_c
        \end{array}
\right)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

where

  * _[eq]#{theta}#_ is 0 degrees for
    ename:VK_SURFACE_TRANSFORM_IDENTITY_BIT_KHR
  * _[eq]#{theta}#_ is 90 degrees for
    ename:VK_SURFACE_TRANSFORM_ROTATE_90_BIT_KHR
  * _[eq]#{theta}#_ is 180 degrees for
    ename:VK_SURFACE_TRANSFORM_ROTATE_180_BIT_KHR
  * _[eq]#{theta}#_ is 270 degrees for
    ename:VK_SURFACE_TRANSFORM_ROTATE_270_BIT_KHR


The transformed vertex's normalized device coordinates are
[latexmath]
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
\left(
        \begin{array}{c}
                x_d \\
                y_d \\
                z_d
        \end{array}
\right) =
\left(
        \begin{array}{c}
                \frac{x_{c_{trans}}}{w_c} \\
                \frac{y_{c_{trans}}}{w_c} \\
                \frac{z_{c_{trans}}}{w_c}
        \end{array}
\right)
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


When render pass transform is enabled for a render pass instance, the
following additional features are enabled:

  * Each slink:VkViewport specified by either
    slink:VkPipelineViewportStateCreateInfo::pname:pViewports or
    flink:vkCmdSetViewport will have its width/height [eq]#(p~x~, p~y~)# and
    its center [eq]#(o~x~, o~y~)# similarly transformed by the
    implementation.
  * Each scissor specified by
    slink:VkPipelineViewportStateCreateInfo::pname:pScissors or
    flink:vkCmdSetScissor will have its [eq]#(offset~x~, offset~y~)# and
    [eq]#(extent~x~, extent~y~)# similarly transformed by the
    implementation.
  * The pname:renderArea specified in
    slink:VkCommandBufferInheritanceRenderPassTransformInfoQCOM and
    slink:VkRenderPassBeginInfo will be similarly transformed by the
    implementation.
  * The [eq]#(x, y)# components of shader variables with built-in
    decorations code:FragCoord, code:SamplePosition, or code:PointCoord will
    be similarly transformed by the implementation.
  * The [eq]#(x,y)# components of the code:offset operand of the
    code:InterpolateAtOffset extended instruction will be similarly
    transformed by the implementation.
  * The values returned by SPIR-V <<shaders-derivative-operations,
    derivative instructions>> code:OpDPdx, code:OpDPdy, code:OpDPdxCourse,
    code:OpDPdyCourse, code:OpDPdxFine, code:OpDPdyFine will be similarly
    transformed by the implementation.


The net result of the above, is that applications can: act as if rendering
to a framebuffer oriented with the
slink:VkSurfaceCapabilitiesKHR::pname:currentTransform.
In other words, applications can: act as if the presentation engine will be
performing the transformation of the swapchain image after rendering and
prior to presentation to the user.
In fact, the transformation of the various items cited above are being
handled by the implementation as the rendering takes place.

endif::VK_QCOM_render_pass_transform[]


[[vertexpostproc-viewport]]
== Controlling the Viewport

The viewport transformation is determined by the selected viewport's width
and height in pixels, [eq]#p~x~# and [eq]#p~y~#, respectively, and its
center [eq]#(o~x~, o~y~)# (also in pixels), as well as its depth range min
and max determining a depth range scale value [eq]#p~z~# and a depth range
bias value [eq]#o~z~# (defined below).
The vertex's framebuffer coordinates [eq]#(x~f~, y~f~, z~f~)# are given by

  {empty}:: [eq]#x~f~ = (p~x~ / 2) x~d~ {plus} o~x~#
  {empty}:: [eq]#y~f~ = (p~y~ / 2) y~d~ {plus} o~y~#
  {empty}:: [eq]#z~f~ = p~z~ {times} z~d~ {plus} o~z~#

Multiple viewports are available, numbered zero up to
sname:VkPhysicalDeviceLimits::pname:maxViewports minus one.
The number of viewports used by a pipeline is controlled by the
pname:viewportCount member of the sname:VkPipelineViewportStateCreateInfo
structure used in pipeline creation.

[eq]#x~f~# and [eq]#y~f~# have limited precision, where the number of
fractional bits retained is specified by
sname:VkPhysicalDeviceLimits::pname:subPixelPrecisionBits.
ifdef::VK_EXT_line_rasterization[]
When rasterizing <<primsrast-lines,line segments>>, the number of fractional
bits is specified by
sname:VkPhysicalDeviceLineRasterizationPropertiesEXT::pname:lineSubPixelPrecisionBits.
endif::VK_EXT_line_rasterization[]

[open,refpage='VkPipelineViewportStateCreateInfo',desc='Structure specifying parameters of a newly created pipeline viewport state',type='structs']
--
The sname:VkPipelineViewportStateCreateInfo structure is defined as:

include::{generated}/api/structs/VkPipelineViewportStateCreateInfo.txt[]

  * pname:sType is the type of this structure.
  * pname:pNext is `NULL` or a pointer to a structure extending this
    structure.
  * pname:flags is reserved for future use.
  * pname:viewportCount is the number of viewports used by the pipeline.
  * pname:pViewports is a pointer to an array of slink:VkViewport
    structures, defining the viewport transforms.
    If the viewport state is dynamic, this member is ignored.
  * pname:scissorCount is the number of <<fragops-scissor,scissors>> and
    must: match the number of viewports.
  * pname:pScissors is a pointer to an array of slink:VkRect2D structures
    defining the rectangular bounds of the scissor for the corresponding
    viewport.
    If the scissor state is dynamic, this member is ignored.

.Valid Usage
****
  * [[VUID-VkPipelineViewportStateCreateInfo-viewportCount-01216]]
    If the <<features-multiViewport,multiple viewports>> feature is not
    enabled, pname:viewportCount must: not be greater than `1`
  * [[VUID-VkPipelineViewportStateCreateInfo-scissorCount-01217]]
    If the <<features-multiViewport,multiple viewports>> feature is not
    enabled, pname:scissorCount must: not be greater than `1`
  * [[VUID-VkPipelineViewportStateCreateInfo-viewportCount-01218]]
    pname:viewportCount must: be less than or equal to
    sname:VkPhysicalDeviceLimits::pname:maxViewports
  * [[VUID-VkPipelineViewportStateCreateInfo-scissorCount-01219]]
    pname:scissorCount must: be less than or equal to
    sname:VkPhysicalDeviceLimits::pname:maxViewports
ifndef::VK_EXT_extended_dynamic_state[]
  * [[VUID-VkPipelineViewportStateCreateInfo-scissorCount-01220]]
    pname:scissorCount and pname:viewportCount must: be identical
endif::VK_EXT_extended_dynamic_state[]
  * [[VUID-VkPipelineViewportStateCreateInfo-x-02821]]
    The pname:x and pname:y members of pname:offset member of any element of
    pname:pScissors must: be greater than or equal to `0`
  * [[VUID-VkPipelineViewportStateCreateInfo-offset-02822]]
    Evaluation of [eq]#(pname:offset.x {plus} pname:extent.width)# must: not
    cause a signed integer addition overflow for any element of
    pname:pScissors
  * [[VUID-VkPipelineViewportStateCreateInfo-offset-02823]]
    Evaluation of [eq]#(pname:offset.y {plus} pname:extent.height)# must:
    not cause a signed integer addition overflow for any element of
    pname:pScissors
ifndef::VK_EXT_extended_dynamic_state[]
  * [[VUID-VkPipelineViewportStateCreateInfo-viewportCount-arraylength]]
    pname:viewportCount must: be greater than `0`
  * [[VUID-VkPipelineViewportStateCreateInfo-scissorCount-arraylength]]
    pname:scissorCount must: be greater than `0`
endif::VK_EXT_extended_dynamic_state[]
ifdef::VK_EXT_extended_dynamic_state[]
  * [[VUID-VkPipelineViewportStateCreateInfo-scissorCount-04134]]
    If the graphics pipeline is being created without
    ename:VK_DYNAMIC_STATE_VIEWPORT_WITH_COUNT_EXT and
    ename:VK_DYNAMIC_STATE_SCISSOR_WITH_COUNT_EXT set then
    pname:scissorCount and pname:viewportCount must: be identical
  * [[VUID-VkPipelineViewportStateCreateInfo-viewportCount-04135]]
    If the graphics pipeline is being created with
    ename:VK_DYNAMIC_STATE_VIEWPORT_WITH_COUNT_EXT set then
    pname:viewportCount must: be `0`, otherwise it must: be greater than `0`
  * [[VUID-VkPipelineViewportStateCreateInfo-scissorCount-04136]]
    If the graphics pipeline is being created with
    ename:VK_DYNAMIC_STATE_SCISSOR_WITH_COUNT_EXT set then
    pname:scissorCount must: be `0`, otherwise it must: be greater than `0`
endif::VK_EXT_extended_dynamic_state[]
ifdef::VK_NV_clip_space_w_scaling[]
  * [[VUID-VkPipelineViewportStateCreateInfo-viewportWScalingEnable-01726]]
    If the pname:viewportWScalingEnable member of a
    slink:VkPipelineViewportWScalingStateCreateInfoNV structure included in
    the pname:pNext chain is ename:VK_TRUE, the pname:viewportCount member
    of the slink:VkPipelineViewportWScalingStateCreateInfoNV structure must:
    be greater than or equal to
    slink:VkPipelineViewportStateCreateInfo::pname:viewportCount
endif::VK_NV_clip_space_w_scaling[]
****

include::{generated}/validity/structs/VkPipelineViewportStateCreateInfo.txt[]
--

ifdef::VK_EXT_extended_dynamic_state[]
[open,refpage='vkCmdSetViewportWithCountEXT',desc='Set the viewport count and viewports dynamically for a command buffer',type='protos']
--
To <<pipelines-dynamic-state, dynamically set>> the viewport count and
viewports, call:

include::{generated}/api/protos/vkCmdSetViewportWithCountEXT.txt[]

  * pname:commandBuffer is the command buffer into which the command will be
    recorded.
  * pname:viewportCount specifies the viewport count.
  * pname:pViewports specifies the viewports to use for drawing.

This command sets the viewport count and viewports state for subsequent
drawing commands when the graphics pipeline is created with
ename:VK_DYNAMIC_STATE_VIEWPORT_WITH_COUNT_EXT set in
slink:VkPipelineDynamicStateCreateInfo::pname:pDynamicStates.
Otherwise, this state is specified by the corresponding
slink:VkPipelineViewportStateCreateInfo::pname:viewportCount and
pname:pViewports values used to create the currently active pipeline.

.Valid Usage
****
  * [[VUID-vkCmdSetViewportWithCountEXT-None-03393]]
    The <<features-extendedDynamicState, extendedDynamicState>> feature
    must: be enabled
  * [[VUID-vkCmdSetViewportWithCountEXT-viewportCount-03394]]
    pname:viewportCount must: be between `1` and
    sname:VkPhysicalDeviceLimits::pname:maxViewports, inclusive
  * [[VUID-vkCmdSetViewportWithCountEXT-viewportCount-03395]]
    If the <<features-multiViewport,multiple viewports>> feature is not
    enabled, pname:viewportCount must: be `1`
ifdef::VK_NV_inherited_viewport_scissor[]
  * [[VUID-vkCmdSetViewportWithCountEXT-commandBuffer-04819]]
    pname:commandBuffer must: not have
    slink:VkCommandBufferInheritanceViewportScissorInfoNV::pname:viewportScissor2D
    enabled
endif::VK_NV_inherited_viewport_scissor[]
****

include::{generated}/validity/protos/vkCmdSetViewportWithCountEXT.txt[]
--

[open,refpage='vkCmdSetScissorWithCountEXT',desc='Set the scissor count and scissor rectangular bounds dynamically for a command buffer',type='protos']
--
To <<pipelines-dynamic-state, dynamically set>> the scissor count and
scissor rectangular bounds, call:

include::{generated}/api/protos/vkCmdSetScissorWithCountEXT.txt[]

  * pname:commandBuffer is the command buffer into which the command will be
    recorded.
  * pname:scissorCount specifies the scissor count.
  * pname:pScissors specifies the scissors to use for drawing.

This command sets the scissor count and scissor rectangular bounds state for
subsequence drawing commands when the graphics pipeline is created with
ename:VK_DYNAMIC_STATE_SCISSOR_WITH_COUNT_EXT set in
slink:VkPipelineDynamicStateCreateInfo::pname:pDynamicStates.
Otherwise, this state is specified by the corresponding
slink:VkPipelineViewportStateCreateInfo::pname:scissorCount and
pname:pScissors values used to create the currently active pipeline.

.Valid Usage
****
  * [[VUID-vkCmdSetScissorWithCountEXT-None-03396]]
    The <<features-extendedDynamicState, extendedDynamicState>> feature
    must: be enabled
  * [[VUID-vkCmdSetScissorWithCountEXT-scissorCount-03397]]
    pname:scissorCount must: be between `1` and
    sname:VkPhysicalDeviceLimits::pname:maxViewports, inclusive
  * [[VUID-vkCmdSetScissorWithCountEXT-scissorCount-03398]]
    If the <<features-multiViewport,multiple viewports>> feature is not
    enabled, pname:scissorCount must: be `1`
  * [[VUID-vkCmdSetScissorWithCountEXT-x-03399]]
    The pname:x and pname:y members of pname:offset member of any element of
    pname:pScissors must: be greater than or equal to `0`
  * [[VUID-vkCmdSetScissorWithCountEXT-offset-03400]]
    Evaluation of [eq]#(pname:offset.x {plus} pname:extent.width)# must: not
    cause a signed integer addition overflow for any element of
    pname:pScissors
  * [[VUID-vkCmdSetScissorWithCountEXT-offset-03401]]
    Evaluation of [eq]#(pname:offset.y {plus} pname:extent.height)# must:
    not cause a signed integer addition overflow for any element of
    pname:pScissors
ifdef::VK_NV_inherited_viewport_scissor[]
  * [[VUID-vkCmdSetScissorWithCountEXT-commandBuffer-04820]]
    pname:commandBuffer must: not have
    slink:VkCommandBufferInheritanceViewportScissorInfoNV::pname:viewportScissor2D
    enabled
endif::VK_NV_inherited_viewport_scissor[]
****

include::{generated}/validity/protos/vkCmdSetScissorWithCountEXT.txt[]
--
endif::VK_EXT_extended_dynamic_state[]

[open,refpage='VkPipelineViewportStateCreateFlags',desc='Reserved for future use',type='flags']
--
include::{generated}/api/flags/VkPipelineViewportStateCreateFlags.txt[]

tname:VkPipelineViewportStateCreateFlags is a bitmask type for setting a
mask, but is currently reserved for future use.
--

ifndef::VK_VERSION_1_2,VK_EXT_shader_viewport_index_layer,VK_NV_viewport_array2[]
If a geometry shader is active and has an output variable decorated with
code:ViewportIndex, the viewport transformation uses the viewport
corresponding to the value assigned to code:ViewportIndex taken from an
implementation-dependent vertex of each primitive.
If code:ViewportIndex is outside the range zero to pname:viewportCount minus
one for a primitive, or if the geometry shader did not assign a value to
code:ViewportIndex for all vertices of a primitive due to flow control, the
values resulting from the viewport transformation of the vertices of such
primitives are undefined:.
If no geometry shader is active, or if the geometry shader does not have an
output decorated with code:ViewportIndex, the viewport numbered zero is used
by the viewport transformation.
endif::VK_VERSION_1_2,VK_EXT_shader_viewport_index_layer,VK_NV_viewport_array2[]

ifdef::VK_VERSION_1_2,VK_EXT_shader_viewport_index_layer,VK_NV_viewport_array2[]
ifdef::VK_NV_viewport_array2[]
A _<<pipeline-graphics-subsets-pre-rasterization,pre-rasterization shader
stage>>_ can: direct each primitive to zero or more viewports.
The destination viewports for a primitive are selected by the last active
<<pipeline-graphics-subsets-pre-rasterization,pre-rasterization shader
stage>> that has an output variable decorated with code:ViewportIndex
(selecting a single viewport) or code:ViewportMaskNV (selecting multiple
viewports).
The viewport transform uses the viewport corresponding to either the value
assigned to code:ViewportIndex or one of the bits set in
code:ViewportMaskNV, and taken from an implementation-dependent vertex of
each primitive.
If code:ViewportIndex or any of the bits in code:ViewportMaskNV are outside
the range zero to pname:viewportCount minus one for a primitive, or if the
last active <<pipeline-graphics-subsets-pre-rasterization,pre-rasterization
shader stage>> did not assign a value to either code:ViewportIndex or
code:ViewportMaskNV for all vertices of a primitive due to flow control, the
values resulting from the viewport transformation of the vertices of such
primitives are undefined:.
If the last <<pipeline-graphics-subsets-pre-rasterization,pre-rasterization
shader stage>> does not have an output decorated with code:ViewportIndex or
code:ViewportMaskNV, the viewport numbered zero is used by the viewport
transformation.
endif::VK_NV_viewport_array2[]
ifndef::VK_NV_viewport_array2[]
A _<<pipeline-graphics-subsets-pre-rasterization,pre-rasterization shader
stage>>_ can: direct each primitive to one of several viewports.
The destination viewport for a primitive is selected by the last active
<<pipeline-graphics-subsets-pre-rasterization,pre-rasterization shader
stage>> that has an output variable decorated with code:ViewportIndex.
The viewport transform uses the viewport corresponding to the value assigned
to code:ViewportIndex, and taken from an implementation-dependent vertex of
each primitive.
If code:ViewportIndex is outside the range zero to pname:viewportCount minus
one for a primitive, or if the last active
<<pipeline-graphics-subsets-pre-rasterization,pre-rasterization shader
stage>> did not assign a value to code:ViewportIndex for all vertices of a
primitive due to flow control, the values resulting from the viewport
transformation of the vertices of such primitives are undefined:.
If the last <<pipeline-graphics-subsets-pre-rasterization,pre-rasterization
shader stage>> does not have an output decorated with code:ViewportIndex,
the viewport numbered zero is used by the viewport transformation.
endif::VK_NV_viewport_array2[]
endif::VK_VERSION_1_2,VK_EXT_shader_viewport_index_layer,VK_NV_viewport_array2[]

A single vertex can: be used in more than one individual primitive, in
primitives such as ename:VK_PRIMITIVE_TOPOLOGY_TRIANGLE_STRIP.
In this case, the viewport transformation is applied separately for each
primitive.

[open,refpage='vkCmdSetViewport',desc='Set the viewport dynamically for a command buffer',type='protos']
--
To <<pipelines-dynamic-state, dynamically set>> the viewport transformation
parameters, call:

include::{generated}/api/protos/vkCmdSetViewport.txt[]

  * pname:commandBuffer is the command buffer into which the command will be
    recorded.
  * pname:firstViewport is the index of the first viewport whose parameters
    are updated by the command.
  * pname:viewportCount is the number of viewports whose parameters are
    updated by the command.
  * pname:pViewports is a pointer to an array of slink:VkViewport structures
    specifying viewport parameters.

This command sets the viewport transformation parameters state for
subsequent drawing commands when the graphics pipeline is created with
ename:VK_DYNAMIC_STATE_VIEWPORT set in
slink:VkPipelineDynamicStateCreateInfo::pname:pDynamicStates.
Otherwise, this state is specified by the
sname:VkPipelineViewportStateCreateInfo::pname:pViewports values used to
create the currently active pipeline.

The viewport parameters taken from element [eq]#i# of pname:pViewports
replace the current state for the viewport index [eq]#pname:firstViewport
{plus} i#, for [eq]#i# in [eq]#[0, pname:viewportCount)#.

.Valid Usage
****
  * [[VUID-vkCmdSetViewport-firstViewport-01223]]
    The sum of pname:firstViewport and pname:viewportCount must: be between
    `1` and sname:VkPhysicalDeviceLimits::pname:maxViewports, inclusive
  * [[VUID-vkCmdSetViewport-firstViewport-01224]]
    If the <<features-multiViewport,multiple viewports>> feature is not
    enabled, pname:firstViewport must: be `0`
  * [[VUID-vkCmdSetViewport-viewportCount-01225]]
    If the <<features-multiViewport,multiple viewports>> feature is not
    enabled, pname:viewportCount must: be `1`
ifdef::VK_NV_inherited_viewport_scissor[]
  * [[VUID-vkCmdSetViewport-commandBuffer-04821]]
    pname:commandBuffer must: not have
    slink:VkCommandBufferInheritanceViewportScissorInfoNV::pname:viewportScissor2D
    enabled
endif::VK_NV_inherited_viewport_scissor[]
****

include::{generated}/validity/protos/vkCmdSetViewport.txt[]
--

Both slink:VkPipelineViewportStateCreateInfo and flink:vkCmdSetViewport use
sname:VkViewport to set the viewport transformation parameters.

[open,refpage='VkViewport',desc='Structure specifying a viewport',type='structs']
--
The sname:VkViewport structure is defined as:

include::{generated}/api/structs/VkViewport.txt[]

  * pname:x and pname:y are the viewport's upper left corner [eq]#(x,y)#.
  * pname:width and pname:height are the viewport's width and height,
    respectively.
  * pname:minDepth and pname:maxDepth are the depth range for the viewport.

[NOTE]
.Note
====
Despite their names, pname:minDepth can: be less than, equal to, or greater
than pname:maxDepth.
====

The framebuffer depth coordinate [eq]#pname:z~f~# may: be represented using
either a fixed-point or floating-point representation.
However, a floating-point representation must: be used if the depth/stencil
attachment has a floating-point depth component.
If an [eq]#m#-bit fixed-point representation is used, we assume that it
represents each value latexmath:[\frac{k}{2^m - 1}], where [eq]#k {elem} {
0, 1, ..., 2^m^-1 }#, as [eq]#k# (e.g. 1.0 is represented in binary as a
string of all ones).

The viewport parameters shown in the above equations are found from these
values as

  {empty}:: [eq]#o~x~ = pname:x {plus} pname:width / 2#
  {empty}:: [eq]#o~y~ = pname:y {plus} pname:height / 2#
  {empty}:: [eq]#o~z~ = pname:minDepth#
  {empty}:: [eq]#p~x~ = pname:width#
  {empty}:: [eq]#p~y~ = pname:height#
  {empty}:: [eq]#p~z~ = pname:maxDepth - pname:minDepth#.

ifdef::VK_QCOM_render_pass_transform[]
If a render pass transform is enabled, the values [eq]#(p~x~,p~y~)# and
[eq]#(o~x~, o~y~)# defining the viewport are transformed as described in
<<vertexpostproc-renderpass-transform, render pass transform>> before
participating in the viewport transform.
endif::VK_QCOM_render_pass_transform[]

ifdef::VK_VERSION_1_1,VK_KHR_maintenance1[]
The application can: specify a negative term for pname:height, which has the
effect of negating the y coordinate in clip space before performing the
transform.
When using a negative pname:height, the application should: also adjust the
pname:y value to point to the lower left corner of the viewport instead of
the upper left corner.
Using the negative pname:height allows the application to avoid having to
negate the y component of the code:Position output from the last
<<pipeline-graphics-subsets-pre-rasterization,pre-rasterization shader
stage>>.
endif::VK_VERSION_1_1,VK_KHR_maintenance1[]

The width and height of the <<limits-maxViewportDimensions,
implementation-dependent maximum viewport dimensions>> must: be greater than
or equal to the width and height of the largest image which can: be created
and attached to a framebuffer.

The floating-point viewport bounds are represented with an
<<limits-viewportSubPixelBits,implementation-dependent precision>>.

.Valid Usage
****
  * [[VUID-VkViewport-width-01770]]
    pname:width must: be greater than `0.0`
  * [[VUID-VkViewport-width-01771]]
    pname:width must: be less than or equal to
    sname:VkPhysicalDeviceLimits::pname:maxViewportDimensions[0]
ifndef::VK_VERSION_1_1,VK_KHR_maintenance1,VK_AMD_negative_viewport_height[]
  * [[VUID-VkViewport-height-01772]]
    pname:height must: be greater than `0.0`
endif::VK_VERSION_1_1,VK_KHR_maintenance1,VK_AMD_negative_viewport_height[]
  * [[VUID-VkViewport-height-01773]]
    The absolute value of pname:height must: be less than or equal to
    sname:VkPhysicalDeviceLimits::pname:maxViewportDimensions[1]
  * [[VUID-VkViewport-x-01774]]
    pname:x must: be greater than or equal to pname:viewportBoundsRange[0]
  * [[VUID-VkViewport-x-01232]]
    [eq]#(pname:x {plus} pname:width)# must: be less than or equal to
    pname:viewportBoundsRange[1]
  * [[VUID-VkViewport-y-01775]]
    pname:y must: be greater than or equal to pname:viewportBoundsRange[0]
ifdef::VK_VERSION_1_1,VK_KHR_maintenance1,VK_AMD_negative_viewport_height[]
  * [[VUID-VkViewport-y-01776]]
    pname:y must: be less than or equal to pname:viewportBoundsRange[1]
  * [[VUID-VkViewport-y-01777]]
    [eq]#(pname:y {plus} pname:height)# must: be greater than or equal to
    pname:viewportBoundsRange[0]
endif::VK_VERSION_1_1,VK_KHR_maintenance1,VK_AMD_negative_viewport_height[]
  * [[VUID-VkViewport-y-01233]]
    [eq]#(pname:y {plus} pname:height)# must: be less than or equal to
    pname:viewportBoundsRange[1]
ifdef::VK_EXT_depth_range_unrestricted[]
  * [[VUID-VkViewport-minDepth-01234]]
    Unless `apiext:VK_EXT_depth_range_unrestricted` extension is enabled
    pname:minDepth must: be between `0.0` and `1.0`, inclusive
endif::VK_EXT_depth_range_unrestricted[]
ifndef::VK_EXT_depth_range_unrestricted[]
  * [[VUID-VkViewport-minDepth-02540]]
    pname:minDepth must: be between `0.0` and `1.0`, inclusive
endif::VK_EXT_depth_range_unrestricted[]
ifdef::VK_EXT_depth_range_unrestricted[]
  * [[VUID-VkViewport-maxDepth-01235]]
    Unless `apiext:VK_EXT_depth_range_unrestricted` extension is enabled
    pname:maxDepth must: be between `0.0` and `1.0`, inclusive
endif::VK_EXT_depth_range_unrestricted[]
ifndef::VK_EXT_depth_range_unrestricted[]
  * [[VUID-VkViewport-maxDepth-02541]]
    pname:maxDepth must: be between `0.0` and `1.0`, inclusive
endif::VK_EXT_depth_range_unrestricted[]
****

include::{generated}/validity/structs/VkViewport.txt[]
--